The present invention is in the field of anechoic chambers suitable for evaluating and measuring the characteristics and properties of antennas and other electronic devices.
This invention relates to methods and apparatus useful in measurement and testing of antennas and other electronic devices. More specifically, this invention relates to an improved tapered anechoic chamber that significantly lowers scattering effects and allows for easy rotation of the feed antenna.
The tapered chamber concept was introduced many years ago. It was originally developed to reduce stray signals normally associated with traditional rectangular chambers by placing the feed antenna at the throat of a tapered section. The antenna must then radiate a field that does not illuminate the walls, as it would not satisfy the necessary electromagnetic boundary conditions.
Unfortunately, the basic chamber design has several problems. First, authors of the original concept did not actually have a broadband feed antenna that could satisfy the boundary conditions in this application. As a result, multiple feeds had to be used and moved around in the throat region to get the proper field quality in the test zone. The original tapered chamber also assumed that the sidewall absorber had to be smooth wedge absorber, as shown in FIG. 1, continuous from the feed area to the back wall of the chamber 1. In practice this has not been the case, as a test object 2 tends to scatter incident energy 3 toward 4 the walls, ceiling, and floor. This energy is then strongly scattered by wedge absorber 5 back to the test object 2.
To correct this situation, FIG. 2 shows that tapered chambers 7 today normally have pyramidal absorber 8 mounted on the walls, ceiling, and floor surrounding the test zone. These absorber layout schemes, however, similarly lead to undesired scattered signal effects. An improved absorber scheme is desired.
Tapered chambers are normally used for low frequency measurements, which requires the back wall pyramidal absorber to be quite thick using current absorber layout schemes. This leads to long chambers and absorber that deteriorates with time, as the pyramid tips tend to droop due to their size and weight.
Also, there exists a complex problem with the feed antenna. The phase center of the antenna is preferably at the vertex of the absorber-lined chamber. At first glance this might seem impossible, as the surrounding absorber would tend to attenuate the input energy from the feed. To avoid this situation, tapered chamber manufacturers today use log periodic or horn antennas displaced from the vertex of the tapered chamber. This in turn leads to some of the same problems observed in rectangular chambers. As the feed antenna illuminates the walls, undesired stray energy is scattered into the test zone.
Another issue with this chamber/feed antenna design involves changing the polarization of the feed antenna. Since the feed is inherently surrounded by specifically-designed absorber at the throat of the tapered section, rotating the feed antenna is not possible in a rigid chamber.
It is therefore an object of the present invention to develop a tapered anechoic chamber that minimizes undesired signal scattering, minimizes chamber length, and minimizes absorber deterioration, while at the same time allowing easy rotation of the feed antenna.
Although described with respect to the field of electromagnetic measurement, it will be appreciated that similar advantages may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes tapered anechoic chambers and chamber systems. This invention also includes machines or electronic apparatus using these aspects of the invention. The present invention may also be used to upgrade, repair or retrofit existing machines or electronic devices or instruments of these types, using methods and components used in the art. The present invention also includes methods and processes for using these devices.
A tapered anechoic chamber of the present invention first comprises a planar back wall having a rectangular shape. The chamber also has a planar front wall comprising a rectangular shape. The planar front wall is positioned parallel to and separated a distance from the back wall. The planar front wall is of smaller dimension than the planar back wall, the center points of the front and back walls lying along a line orthogonal to the planes defined by the walls.
The chamber has four side walls, each of which are connected to a full edge of the planar back wall. Each of the side walls lies in a plane that is orthogonal to the plane defined by the back wall. The four side walls are connected at the adjacent edges so as to form a rectangular enclosure attached to the planar back wall. The chamber also has four tapered side walls. Each of the tapered side walls contacts a full outer edge of one of the side walls and a full edge of the planar front wall. The tapered side walls are then connected at adjacent edges so as to form an enclosed range between the planar front and back walls.
Electromagnetic energy absorbing material is attached to the inside of the enclosed range. The material may be any electromagnetic energy absorbing material known in the art. The material comprises a plurality of tapered members, such as pyramidal or wedge members, extending into the enclosed range. At least one portion of the energy absorbing material comprises a plurality of tapered members wherein adjacent tapered members comprise different lengths from the tip to the base of each member. The tips of the tapered members preferably form a periodic pattern, such as a sinusoidal pattern, semi-sinusoidal pattern, or Chebyshev pattern. The portion of the chamber which has the adjacent tapered members of differing length may be any appropriate portion of the chamber, such as the front wall, back wall, side walls, or tapered side walls.
The chamber may additionally comprise a feed antenna positioned near the front wall in the enclosed range. The chamber may also have a probe antenna positioned between the four side walls of the enclosed range. These antennas may be any appropriate antennas known in the art.
Also included in the present invention is a second tapered anechoic chamber that comprises planar front and back walls, each having a rectangular shape. The front wall is positioned parallel to, and separated a distance from the back wall, and is of a smaller dimension than the back wall. The center points of the front and back walls lie along a line orthogonal to the planes defined by the walls.
The chamber comprises four side walls, each of the-side walls connected to a full edge of the planar back wall. Each side wall lies in a plane orthogonal to the plane defined by the planar back wall. The four side walls are connected so as to form a rectangular enclosure attached to the back wall. The chamber also has four tapered side walls, each of the tapered side walls contacting a full outer edge of one of the side walls and a full edge of the planar front wall. The four tapered side walls are connected so as to form an enclosed range between the front and back walls.
The chamber has an electromagnetic energy absorbing material attached to the inside of the enclosed range. This may be any appropriate material known in the art. A TEM antenna extends into the enclosed range from the planar front wall. A resistive card then terminates the TEM antenna in the enclosed range. The resistive card may be any appropriate card with an appropriate resistivity. The chamber may additionally comprise a probe antenna positioned between the four side walls in the enclosed range.
The present invention also includes another tapered anechoic chamber. This chamber comprises planar front and back walls, each wall having a rectangular shape. The planar front wall is positioned parallel to and separated a distance from the back wall, the front wall having a dimension smaller than the back wall. The center points of the front and back walls lie along a line orthogonal to the planes defined by these walls.
The chamber comprises four side walls, each of which is connected to a full edge of the planar back wall. Each side wall lies in a plane orthogonal to the plane defined by the planar back wall. The four side walls are connected at adjacent edges so as to form a rectangular enclosure attached to the planar back wall. The chamber also has four tapered planar rear side portions, each of which contacts a full outer edge of one of the side walls. Each of the tapered rear side portions lies in a plane defined by an outer edge of one of the side walls and an edge of the planar front wall. The tapered planar rear side portions are connected at adjacent edges so as to define an open-ended range.
The chamber also comprises four tapered planar front side portions, each of which contacts a full edge of the planar front wall. Each of the tapered front side portions lies in a plane defined by an outer edge of one of the side walls and an edge of the planar front wall. The tapered planar front side portions are connected so as to define an open-ended tip separated from the open-ended range.
Electromagnetic energy absorbing material is attached to the inside of the open-ended range and the open-ended tip. The material may be any appropriate electromagnetic energy absorbing material known in the art. A system of rollers is positioned between the open-ended range and the open-ended tip. The system of rollers is preferably adapted to allow rotation of the open-ended tip relative to the open-ended range. The range may additionally comprise a feed antenna positioned between the tapered planar front side portions or a probe antenna positioned between the four side walls.
The present invention contains another tapered anechoic chamber. This chamber comprises planar front and back walls, each having a rectangular shape. The front wall is separated a distance from the back wall, and comprises a smaller dimension. The center points of the walls lie along a line orthogonal to the planes defined by the walls.
The chamber has four side walls, each of which is connected to a full edge of the planar back wall. Each side wall lies in a plane orthogonal to the plane defined by the planar back wall. The four side walls are connected so as to form a rectangular enclosure attached to the planar back wall. The chamber also has four tapered planar rear side portions, each of which contacts a full outer edge of one of the side walls. Each of the tapered rear side portions lies in a plane defined by an outer edge of one of the side walls and an edge of the planar front wall. The tapered planar rear side portions are connected so as to define an open-ended range.
The chamber has four tapered planar front side portions, each of which contacts a full edge of the planar front wall. Each tapered front side portions lies in a plane defined by an outer edge of one of the side walls and an edge of the planar front wall. The tapered planar front side portions are connected so as to define an open-ended tip separated from the open-ended range.
Electromagnetic energy absorbing material is attached to the inside of the open ended range and the open ended tip. The material comprises a plurality of tapered members extending into the open ended range and the open ended tip. At least one portion of the electromagnetic energy-absorbing material comprises a plurality of tapered members wherein adjacent tapered members comprise different lengths from the tip to the base of each pyramidal member. The tips of the tapered members preferably form a periodic pattern, such as a sinusoidal pattern, semi-sinusoidal pattern, or Chebyshev pattern.
A system of rollers is positioned between the open-ended range and the open-ended tip, preferably adapted to allow rotation of the open-ended tip relative to the open ended range. A TEM antenna extends into the area of the open-ended tip from the planar front wall. A resistive card or R-card terminates the TEM antenna in the open ended tip. The chamber may also comprise a probe antenna positioned between the four side walls. The probe antenna may be adapted to rotate over a range. There may also be a measurement device in communication with the probe antenna.